The proposed investigations continue an on-going series of studies on the biological roles of free radicals in several inter-related areas. Projected studies on the transitory free radicals which appear in animal tissues during x-irradiation are designed to test and apply an hypothesis regarding the biochemical mechanisms involved in tissue radiation sensitivity, especially with respect to the role of the ascorbic acid free radical and flavins. Projected studies on free radicals in carcinogenesis are concerned with efforts to characterize and if possible isolate free radical agents in normal liver which appear to act as scavengers of the free radical intermediates of carcinogens. Projected studies on the roles of free radicals in yeast metabolism relate to the effects of a series of metabolic parameters on free radical concentration.